A schematic section through the human eye with a schematic enlargement of the retina (University of Utah)

Previous studies showed that younger people who score low on intelligence tests, such as IQ, tend to be at higher risk for poorer health and shorter lifespan.

In the current study, psychological scientists led by Dr Idan Shalev of Duke University wondered whether intelligence might serve as a marker indicating the health of the brain, and specifically the health of the system of blood vessels that provides oxygen and nutrients to the brain.

To investigate the potential link between intelligence and brain health, they borrowed a technology from a somewhat unexpected domain – ophthalmology.

The team used digital retinal imaging to gain a window onto vascular conditions in the brain by looking at the small blood vessels of the retina. Retinal blood vessels share similar size, structure, and function with blood vessels in the brain and can provide a way of examining brain health in living humans.

The researchers examined data from participants taking part in the Dunedin Multidisciplinary Health and Development Study, a longitudinal investigation of health and behavior in over 1,000 people born in Dunedin, New Zealand.

The findings were intriguing: having wider retinal venules was linked with lower IQ scores at age 38, even after the researchers accounted for various health, lifestyle, and environmental risk factors that might have played a role. Participants who had wider retinal venules showed evidence of general cognitive deficits, with lower scores on numerous measures of neurospsychological functioning, including verbal comprehension, perceptual reasoning, working memory, and executive function.

The team revealed that people who had wider venules at age 38 also had lower IQ in childhood, a full 25 years earlier.

“It’s remarkable that venular caliber in the eye is related, however modestly, to mental test scores of individuals in their 30s, and even to IQ scores in childhood,” Dr Idan Shalev and colleagues said.

The findings suggest that the processes linking vascular health and cognitive functioning begin much earlier than previously assumed, years before the onset of dementia and other age-related declines in brain functioning.

The current study doesn’t address the specific mechanisms that drive the relationship between retinal vessels and cognitive functioning, but the researchers surmise that it may have to do with oxygen supply to the brain.

“Increasing knowledge about retinal vessels may enable scientists to develop better diagnosis and treatments to increase the levels of oxygen into the brain and by that, to prevent age-related worsening of cognitive abilities,” the scientists concluded.